Field of the Invention
The present invention relates to an imaging optical element, and is suitable for an optical scanning device included in an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, and a multifunction printer, for example.
Description of the Related Art
As an optical scanning device included in an image forming apparatus, there has been conventionally known the one that optically scans a scanned surface in a main scanning direction by deflecting light beams emitted from a light source, using a deflector, and guiding the deflected light beams to the scanned surface using an imaging optical element. Japanese Patent Application Laid-Open No. 2002-189185 describes an optical scanning device that includes an imaging optical element arranged closer to a deflector, and sets a scanning field angle to a wide field angle for downsizing the entire device.
In the optical scanning device described in Japanese Patent Application Laid-Open No. 2002-189185, however, a light source unit is arranged with protruding in a main scanning direction. That is, the downsizing in the main scanning direction is not considered in the technique. In addition, if the light source unit and a cylindrical lens are brought closer to a deflection means, the optical scanning device described in Japanese Patent Application Laid-Open No. 2002-189185 can be downsized. Nevertheless, if the cylindrical lens is brought closer to the deflection means, an F-number in a sub-scanning cross section needs to increased, so that a sufficient light amount cannot be ensured on a scanned surface.